You are under category 2B because you are an unmarried son or daughter of a Permanent Resident; you aged out of the child category. Generally a child ,under U.S. immigration law , must be 21yrs or younger. You are considered to be under the category that you fit in when the priority date is current and you file for AOS, not necessarily what you fit in when the petition was filed. Your mother might want to consider naturalizing to become a U.S. Citizen. If she does you will be placed in the 1st preference category which might take less time than 2B.
You might want to contact an immigration attorney to discuss all the details of your case for further information.
The above message is general information only and does not create an attorney-client relationship.
Seattle Immigration Attorney
Your turning 21 moves you from the second preference family-based 2A category (unmarried children un¬der the age of 21) to the second preference 2B category (unmarried children over 21 years of age). Please keep in mind that you must remain unmarried to qualify for the second preference category.
The Child Status Protection Act (CSPA) addresses the problem of minor children losing their eligibility for immigration benefits because they had aged-out (turned 21 years old) as a result of processing delays by USCIA or the Department of State. The eligibility of an applicant for benefits under the CSPA may be determined at the time a visa application is adjudicated by a consular officer. Using a set formula, an applicant may remain qualify if his or her CSPA computed age is under 21. Since your visa is still not available, a crude calculation using the available data you provided seems to disqualify you under CSPA.
Hope this answer helps others who are in similar situation but who may qualify under CSPA.